Some plants need soft or acidic water to thrive.
Many domestic water supplies contain calcium and magnesium, which can raise the soil pH.
Water from recognized ‘soft water’ areas can have calcium added at the treatment works to improve its drinking quality.
Avoid giving hard water to ericaceous plants, as water above pH7 can cause chlorosis or yellowing of foliage, thus affecting photosynthesis and the subsequent health of the plant.
There are products on the market that will remove calcium and other impurities from tap water.
Rainwater collected in water butts is slightly acidic and is suitable for most garden plants.
To prevent the formation of algae cover the water butts to keep out sunlight.